There are some really cool effects I want to talk about here! Dense clouds of water droplets scatter light many times, absorbing almost none of the light as it is scattered. This gives rise to phenomena such as bright cloud centres that contrast with dark edges (especially when the sun is behind the camera) and interreflections between masses of cloud at scales both large and small. Terragen 4 can produce these results by simulating multiple scattering much more precisely than Terragen 3. The clouds are also lit by the surrounding atmosphere, which in this video shows up as blue in the shadows. Terragen 3 could approximate this too with GI, but the new model in Terragen 4 shows real detail and self-shadowing of the environment lighting in the areas that the sunlight doesn't reach, and these areas would appear more flat in Terragen 3. The "silver lining" effect which is strongest when the clouds are back-lit is also much better than before.

You might be wondering about the shape of the cloud itself. This is a localised cloud with a few layered fractals to control the shape/density. Terragen 3 can also produce shapes like this, but it would be very difficult to make them look realistic because of the lighting. Until now, lighting has limited the kinds of clouds we can render photo-realistically. One of the goals of Terragen 4 is to remove that barrier. When Terragen 4 ships, we'll include presets or projects to show how to render clouds like this. Another goal of Terragen 4 is to make it easier to use, not just more capable. I hope that it might be possible to create cumulus clouds like these with just a few sliders, not a network of nodes, but that idea is still on the drawing board. Even so, the new lighting will make it easier to get good looking results from simple cloud setups.

When I compared render times between the new and the old lighting model, they were almost exactly the same. That's not always going to be true, but it was in this case. You'll still be able to use the old clouds whenever you want.

The alpha testers know that there are a few kinks that I need to work out with the new clouds, but as I do, we'll be able to render lots more examples to show you what's possible with Terragen 4.

Awesome job Matt. On the long drives I take for my work, I spend a great deal of time looking at phenomena like this and enjoying its beauty and complexity ... and wondering when TG would get to the point that it would be able to create it. Looks like you're really getting there. I really look forward to seeing what the skilled artists here create with it! (Or what they are already creating with it, but just haven't been allowed to share ).

...One of the goals of Terragen 4 is to remove that barrier. When Terragen 4 ships, we'll include presets or projects to show how to render clouds like this. Another goal of Terragen 4 is to make it easier to use, not just more capable. I hope that it might be possible to create cumulus clouds like these with just a few sliders, not a network of nodes, but that idea is still on the drawing board. ...

Really wonderful cloud lighting and curious about the new way to do that kind of clouds Matt.

I saw that tunnel in the clouds right away. You only talked generally about cloud shape in your post. So is that tunnel not as interesting as I first thought? People here have talked about voxels often, it that whats going on here, or just reading too much in?

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I hope that it might be possible to create cumulus clouds like these with just a few sliders, not a network of nodes, but that idea is still on the drawing board.

This drawing board you speak of sounds like my idea of CG heaven. It should be gilded when you are finished with it.

Amazing improvement. I was always looking for a way to achieve more detail in shadowed areas so I'm really happy this is now possible. Can't wait to finally use this in production.

As for generating clouds more easily, it would be great to be able to base cloud shapes on geometry instead of procedurals, although that would require a set of tools to generate the shapes, of course.

I saw that tunnel in the clouds right away. You only talked generally about cloud shape in your post. So is that tunnel not as interesting as I first thought? People here have talked about voxels often, it that whats going on here, or just reading too much in?

The tunnel just happened accidentally from the noise functions. It wasn't caused by anything special to Terragen 4. Voxel-based cloud editing would be nice but we don't have a plan for that yet.

It seems to be based on a spherical gizmo for the cloud boundaries but looks very cool despite being quite basic. I guess a good way to expand this would be to be able to combine several gizmos to form one gizmo, similar to how meta balls work. There are videos showing a similar workflow in Houdini but LW's shading and interactivity looks better here.

Then again, with the new iterative rendering in TG4 we might get a similar functionality so I'm really looking forward to the release.

A bit late in commenting as I saw this off my news feed right to the tube, but already I'm saving for a new computer to parallel the TG4 upgrade. Totally stunning....I think I need a patron hee hee hee